The control of molecular contamination in advanced semiconductor processing is critical to successful manufacturing. The use of very short wavelengths (Extreme Ultraviolet, EUV; 13.5 nm) increases photo-chemical decomposition and subsequent deposition of contaminants on optical parts. The results are yield loss, shortened tool life and reduced long-term device reliability. Therefore, very strict specifications on the out-gassing of organics are imposed on sub-assemblies and parts used in semiconductor manufacturing equipment.
The document US2009/0090197 describes pre-concentrator devices for use in a gas analysis or detector system. Various detachable pre-concentrators may be used in a cascade. The document describes pre-concentration and detection in atmospheric pressure.
In vacuum or low pressure circumstances, it is difficult to pump a sufficient amount of gas through a detection system. In such circumstances it is known to use a pre-concentration device. In a pre-concentration device, the molecular contamination is gathered during a relatively long time span, called a collection phase now. Then, the gathered molecules are released in a relatively short time interval, called a transfer phase now. From an analysis of the released gas, the molecular contamination can be determined.
An example of a known pre-concentration device is shown in FIG. 2. The pre-concentration device is a hollow tube packed with sorbent material. The interconnecting open spaces between the particles in the packed bed can be thought of as a large number of capillaries with a much smaller effective diameter than the device they are packed into. Reduced effective diameter leads to reduced gas flow. In normal circumstances that would not be a problem. However, when working in the molecular or transition flow range (vacuum or very low pressure), a reduced effective diameter may cause bigger problems. Because the conductivity of the device and the gas flow in the molecular and transition flow range are highly dependent on the cross sectional area of the device it must flow through, the gas flow decreases drastically. The inset shows the particles of the sorbent and the path which interconnecting open spaces between the particles in the packed bed can be thought of as a large number of capillaries with a much smaller effective diameter than the device they are packed into. When working in the molecular or transition flow range, the above described pre-concentration device thus has a serious problem with the gas flow, which results in extraordinary long sampling times (e.g. months) when low detections limits are required (e.g. ppbV, pptV).